This invention relates to steering system, specifically steering system for use in oil, gas, geothermal, and/or horizontal drilling. The ability to accurately adjust the direction of drilling in downhole drilling applications is desirable to direct the borehole toward specific targets. A number of steering systems have been devised for this purpose.
One such system is disclosed in U.S. Pat. No. 5,803,185, to Barr, which is herein incorporated by reference for all that it contains. It discloses a steerable rotary drilling system with a bottom-hole assembly which includes, in addition to the drill bit, a modulated bias unit and control unit, the bias unit comprising a number of hydraulic actuators around the periphery of the unit, each having a movable thrust member which is hydraulically displaceable outwardly for engagement with the formation of the borehole being drilled. Each actuator may be connected, through a control valve, to a source of drilling fluid under pressure and the operation of the valve is controlled by the control unit so as to modulate the fluid pressure supplied to the actuators as the bias unit rotates. If the control valve is operated in synchronism with rotation of the bias unit the thrust members impart a lateral bias to the bias unit, and hence to the drill bit, to control the direction of drilling.